Water mains, water pipes of apartment houses or water pipes of factories gradually form scales on the inner surfaces thereof with the passage of time, and this results in decreasing the water supply capability of the pipe. The conventional method commonly employed to prevent the decrease in water supply capability of the pipe is that the inner surface of the pipe is scraped with a sand jet method, and lined, for instance, with paint for protection of the surface.
As a method to protect the inner surface of the pipe after the scraping treatment, the applicant has developed a technique to form a paint film on the inner surface of the pipe with a method in which mixed gas, formed by compressed air and paint, is sprayed inside the pipe to be treated. The mixture of air and paint is sprayed from one end and paint particles from said mixture adhere to the inner surface of the pipe, thus forming a layer of paint as required. This technique has been taught in U.S. Pat. No. 4,327,132.
In the foregoing described technique, a two-component type epoxy resin main agent and a hardening agent are mixed in a mixer to form paint. Thereafter a mixture fluid formed by epoxy resin paint and air is supplied into an accelerating fluid apparatus, and, then, mixed with further compressed air sent from a compressor to form a second mixture fluid. The second mixture fluid is sprayed inside the pipe, for which a lining is to be made, from one end of the pipe, thus forming a paint film with a uniform thickness on the inner surface of the pipe.
Paint particles contained in mixture fluid sprayed inside the pipe make contact with the inner surface of the pipe, and adhere to the surface while moving inside the pipe. Paint particles which adhere to the inner surface in the vicinity of the inlet of the pipe form liquid layers with a certain viscosity, and these layers are pushed forward in response to the force of the second mixture fluid. Accordingly, a lining film is formed from the inlet side to the outlet side of the pipe in order.
The pipe with a comparatively small inner diameter can also be lined by this method. However, it has been found that the fluid pressure is greatly reduced while passing through a pipe with a very small inner diameter, and hence a pipe, in which a worthwhile lining is to be formed by this method, is shortened in length as the inner diameter of the pipe becomes smaller.
If the required thickness of lining is 0.2-1 mm, the maximum length of the pipe to which this method is applied in relation to the inner diameter is as follows:
TABLE I ______________________________________ (1B = 1 inch) Inner Diameter Maximum Length ______________________________________ 1B 50 m 2B 100 m 3B 150 m 4B 200 m ______________________________________
According to other experiments, the optimum ranges of the flow volume of mixture fluid are as follows:
TABLE II ______________________________________ Inner Diameter Optimum Flow Volume ______________________________________ 1B 1.5-2.5 (M.sup.3 /min) 11/4B 2.3-3.9 11/2B 3.4-5.6 2B 6-10 3B 13.5-22.5 4B 24-40 ______________________________________
The afore-mentioned method of lining is easily applied to form a paint film with a uniform thickness on the inner surface of the pipe if the inner diameter of the pipe line is fixed.
While the foregoing works well with pipes of uniform diameter, none of the prior-art techniques works well with pipes of varying diameters. With so-called reduced pipe lines, in which branch pipes are installed and the inner diameter of the pipe line varies at the sections where the branch pipes are installed, a flow volume of mixture fluid passing through the pipes does not remain optimum to match the inner diameter of the pipes at the sections where branch pipes are installed. That is, the flow speed of a mixture fluid will not remain constant throughout the entire length of the pipe line, i.e. the flow will be slower at a section where the diameter is large and faster at a section where the diameter is small, thus resulting in the uneven thickness of a lining film. It is to this problem that the present invention is mainly directed.